It is well known to use a gantry crane 1 of the type illustrated in FIG. 1 to transport a load in a manufacturing plant. For example, gantry cranes 1 are used to transport machine dies 3 for pressing motor vehicle body panels in a sheet metal pressing facility. The crane 1 is operated by a dedicated crane operator and one or more sling operators.
The crane 1 comprises a bridge 9 movable in a longitudinal direction X. A crab unit 11 housing a hoist 13 is movably mounted on the bridge 9 and can travel in a transverse direction Y. A rectangular lifting frame 15 is supported by the hoist 13 and tour slings 17a-d are permanently connected to the lifting frame 15. The four slings 17a-d each have a coupling provided at their free ends (i.e. at the end distal from the lifting frame 15) to be attached to respective fixing points 19a-d on a load such as a press tool or die 3 and secured by a locking pin. Operating the hoist 13 raises and lowers the lifting frame 15, thereby raising and lowering the die 3. The die 3 is transported by moving the bridge 6 and/or the crab unit 11 once the die 3 has been raised.
In view of the loads involved, the transport of the die 3 to and from the die bed is potentially dangerous. When the lifting frame 15 is travelling within the die bed, one of the slings 17a-d could snag a stationary object (such as a die 3) causing it to be displaced. When a lifting operation is initially performed by the hoist 13, one of the slings 17a-d could snag on the die 3 to be lifted and result in an uncontrolled movement. Furthermore, when the die 3 is initially lifted it may be out of balance resulting in an initial displacement or swinging action before the die 3 centres. When the die 3 is travelling, it could collide with a stationary object or another die 3. These are potentially hazardous scenarios and considerable care is required by the crane and sling operators.
The present invention sets out to help ameliorate or overcome at least some of the problems associated with prior art systems.